That has also been the rule in the other states where I’ve undergone that training

For the scenario we’re discussing, the most action that any store employee could have legally taken would have been to ask to see your receipt, to determine whether the milk had been paid for or not. If the cashier had accidentally overlooked it, the most they could have done would have been to simply allow you to pay for it or voluntarily leave it behind. But stalking you, laying in wait, and then forcibly taking something out of your cart, either before or after going through the checkout line, because of suspicions of theft? Any decent attorney representing you would have a field day with that one. Even going to small claims court without formal representation, the judge would be all over the store for inappropriate conduct. And any store manager should know that.